Bacteria that contain magnetosomes display magnetotaxis and align themselve
s to the earth's magnetic held. When magnetotactic bacteria were first isol
ated several decades ago it was presumed that geomagnetic orientation allow
ed magnetotactic bacteria to orient themselves downward towards sediments w
here the habitat is favorable to their growth and metabolism. As more speci
es of magnetotactic bacteria have been isolated and studied, differences in
magnetotactic responses have been observed which suggested that the primar
y role of magnetosomes might simply be to enhance a microorganism's respons
e to gravity. To resolve if gravity influences magnetotactic behavior in ba
cteria, Magnetospirillum magnetotacticum was used to examine magnetotaxis i
n the absence of gravity. Experiments to compare the orientation of bacteri
a to north- or south-pole magnets were conducted in normal gravity and in t
he microgravity environments aboard the Space Shuttle and Space Station MIR
. In each of the microgravity situations studied, bacteria were impaired in
their ability to orient to magnets and the failure to exhibit magnetotaxis
appeared to be a function of the loss of magnetosomes. The disappearance o
f aggregated magnetosomes seemed to correlate with a general loss of cellul
ar integrity in microgravity. (C) 2000 Elsevier Science Ltd. All rights res
erved.